AT&T Labs is a pale shadow of the glory of its predecessors, AT&T Research and Bell Labs. But it still does important work and one is a Web site called the Online Encyclopedia of Integer Sequences (OEIS). Mathematicians and computer scientists, especially those who work in areas such as combinatorics and graph theory, often encounter sequences of numbers and need to know just what they represent. In most cases, figuring this out the hard way amounts to reinventing the wheel.
With OEIS, a researcher can simply enter a string of numbers and find out what is known about it. For example, if you enter 1, 3, 6, 10, 15, the server will tell you that is sequence A000217, the triangular numbers (these are the number of objects that can form an equilateral triangle like the standard arrangement of bowling pins.) OEIS now comprises over 170,000 entries, from relatively common ones like the triangular numbers to items such as Gijswijt’s sequence, A090822, which begins 1,1,2,1,1,2,2,2,3 and goes on for billions of billions of terms before reaching 5.
OEIS began life as a book, The Encyclopedia (originally the Handbook) of Integer Sequences by Neil A.J. Sloane and Simon Plouffe, still in print. Sloane, a mathematician at AT&T, put it online in 1996 and the searchable form immediately became more useful than the print version (though, in my fondness for print, I still own a copy of the book.)
Maintaining OEIS, which continues to grow, has been an exhausting one-man effort for Sloane. So Sloane announced at the Joint Mathematics Meeting in San Francisco that the Web site is being converted into a wiki, which will allow for collaborative maintenance by the mathematical community, and will be run by the non-profit OEIS Foundation with Sloane as president. The new site is oeis.org, though for the moment it just links back to the AT&T site.